Electron Transport Chain

or What about FADH?

Like NADH, FADH contains electons (and energy)
from oxidation reactions. Remember that FADH, however, contains
less energy than does NADH. Because of this, FADH is unable to
donate its electrons to Complex I of the ETC. Instead, FADH
donates its electons to Complex II (you were
probably wondering why we skipped it before). Complex II
eventually passes the electons on to Complex III via ubi. From
then on, the electrons follow the same pathway as do those from
NADH. Complex II, it turns out, does not move protons as the
electons are transported! This means that every NADH that donates
electrons to the ETC will cause more hydrogen ions to be
transferred than does each FADH. Also, note that the electrons
from FADH still end up on oxygen.

In summary

Each NADH donates electrons to Complex I
while each FADH donates electrons to Complex II. Complex
I uses the energy of the electrons to transport hydrogen
ions while Complex II does not.

For each NADH and each FADH that donates
electrons to the ETC, ½ O2 is used and
converted into one water molecule. Thus, to calculate the
totall number of O2 used, add the number of
NADH and FADH and divide by 2.

The primary effect of the ETC is to pump
hydrogen ions out of the mitochondrion so that there is a
concentration gradient for hydrogen ions across the
mitochondrial membrane. NADH causes more hydrogen ions to
be pumped than does FADH.